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Wall hawkweed subgenus identification and control
Information about the noxious weeds in the wall hawkweed subgenus. The wall hawkweed subgenus is also known by the Latin name, Hieracium, subgenus Hieracium.
About this weed
The species in the wall hawkweed subgenus are non-regulated Class B noxious weeds. This means property owners are not required to control these plants on their property, though it is encouraged. The wall hawkweed subgenus is on the Washington quarantine list so it is illegal to buy or sell these plants in the state.
Wall hawkweed subgenus is known as Hieracium, subgenus Hieracium, and it is in the aster family. This subgenus includes smooth (H. laevigatum), common (H. lachenalii), polar (H. atratum), spotted (H. maculatum), and wall (H. murorum) as recommended for control. This designation excludes European hawkweed (H. sabaudum), which is regulated due to its distribution and impacts.
Why it's a problem
Members of the wall hawkweed subgenus spread readily and have negative impacts to rangeland and other habitats. Especially so in mid to upper elevations and areas with low fertility soils. This includes pastures, roadsides, cleared forest and mountain meadows. Hawkweeds may succeed in these sites because they can capture limited nutrients in degraded soils. This allows hawkweeds form monocultures (large areas filled with one species of plant) Large populations lower biodiversity and reduce forage for grazing animals.
Plant description
Non-native hawkweeds may hybridize and can be difficult to tell apart.
General characteristics of hawkweeds
Traits of non-native hawkweeds:
- All perennials (plants that have a 2+ year life cycle)
- Many non‐native hawkweeds have stolons (horizontal plant stems that root and form new plants), but no native Washington hawkweed species have stolons.
- They contain a milky juice
- Flowers are dandelion‐like and yellow or orange
- Leaves and stems are covered with bristly hairs.
- Plants have rosettes (a circular cluster of leaves on ground level)
- The leaves of most hawkweeds persist through flowering
Traits of wall hawkweed subgenus
Distinguishing traits of wall hawkweed subgenus:
- Leaf edges are coarsely toothed or lobed.
- Leaves grow at the base and often on the stems.
- Flowers are always yellow and generally grow in loose, branched clusters.
- Wall hawkweeds reproduce only by seed and do not have stolons.
- The seeds are small with ribs or grooves and have bristles on one end.
Be aware of look-alike plants
The wall hawkweed subgenus can be confused with the meadow (Pilosella) hawkweed subgenus. Generally, plants of the meadow subgenus have stolons (horizonal plant stem that can take root and form new plants), few to no stem leaves, and leaf edges are smooth or minutely toothed. Whereas wall hawkweed typically does not have stolons, has stem leaves, and the leaf edges are toothed or lobed.
When in doubt, take photos and share them with us or report them on iNaturalist or EDDMapS.
What to do if you find it
Property owners in King County are not required to control plants in the wall hawkweed subgenus and we are not generally tracking infestations. The King County Noxious Weed Control Board encourages property owners to remove it where possible and avoid introducing it to new landscapes.
Control methods
In areas with few weeds, it is important to act quickly before they become harder to control. Make a long-term plan as it often takes several years to get rid of most weeds. Start in the least infested areas first and then move into more heavily infested areas. To reduce costs and environmental impacts, please consider a combination of methods. King County’s best management practices have more detailed information for control of hawkweeds.
Small infestations
If there are only a few plants, hand pulling is an option, but the entire root must be removed. Adding fertilizer or managing soil fertility has also been used to control small populations of hawkweed.
Large infestations
Stay safe when using herbicide:
- Always read the label before use.
- Wear a long-sleeved shirt, long pants, shoes, and eye protection.
- Follow state and local regulations.
Spot spraying with selective herbicides can be effective but cleared areas may become reinfested. To compete with any new weeds, consider replanting cleared areas with desirable species. Apply to plants in spring or early summer when they are actively growing and before flowering. Flowering plants can go to seed after being sprayed. Check the area for new plants for several years.
For specific chemical recommendations, please refer to the PNW Pest Management Handbook.
Disposal instructions
Bag all flower heads. If the plants already have seeds, carefully cut the seed head and place in a bag before pulling plants. Dispose of in the household garbage or take to a transfer station. Do not compost or put in yard waste. Never dump plant material in parks or natural areas because weeds can spread from yard waste piles.
Noxious Weed Disposal - Washington State Noxious Weed Control Board